1. Field of the Invention
The disclosed embodiments relate to the field of manufacturing complex structures made of composites that are formed in molds using compacting molding processes , and more particularly, to such structures that are hollow and include internal structures.
2. Description of the Related Art
The inventor is a co-inventor of a method of producing structures of complex shapes of composite materials disclosed in U.S. patent application Ser. No. 12/296,689, filed on Jun. 3, 2009. The method discloses the use of a flexible, elastomeric envelope, also called a bladder, filled with small spherical objects of different diameters that after undergoing evacuation of air, form a rigid mandrel for laying up dry fiber, prepreg, or film resin to create composite laminated layers on the inner cavity of a composite part. During setup, the bladder is made into a rigid mandrel by filling it with spherical objects and then evacuating the air inside the bladder to compact the spherical objects. The bladder is then sealed to maintain a vacuum which forms a compact, temporary rigid mandrel upon which composite layers can be laid. When the mold is heated, the bladder located inside the part is filled with compressed air causing it to expand and evenly apply a uniform, compaction force to the inside surfaces of the part's interior cavity. Different envelopes may be used that undergo different amounts of expansion when heated to produce different shape bladders that form different wall thicknesses
After compaction, the part is then allowed to cure under regulated air or nitrogen pressure. After curing, air is allowed to enter the envelope causing the envelope t relax and return to its original, flexible state. The envelope is then removed from the part.
Many industries use hollow, complex-shaped, lightweight parts made of composite material that must be precisely manufactured to pre-determined specifications. Not only must the outer surfaces of parts be manufactured to the desired specifications, but the inside and interior walls of the part must be precisely shaped and formed so that exterior and interior walls in the part have the desired thicknesses. It is important that sufficient compaction be used to eliminate porosity in the composite layers. An example of a hollow, complex-shaped, lightweight part made of composite material is a windmill blade.
U.S. Pat. No. 7,473,385 discloses a method of manufacturing hollow windmill blades that includes the use of molds that compact the laminated layers and the use of infused resin. The blade includes a continuous thin outer layer that forms an upper and lower blade sections that surround a hollow cavity. Located inside the hollow cavity is a supporting shear web that extends between the upper and lower sections of the blade. The upper and lower sections of the blade has a layered, sandwich construction comprising an upper fiber layer and a lower fiber layer surrounding an inner passageway that is filled with infused resin , film infusion or pre-preg material.
The shear spar is formed by placing two removable jig plates on opposite sides of the shear spar and the inside the inner cavity. The two jig plates are located in the spaces located on opposite sides of the shear web to be constructed therein to create a compaction force when the envelope or the bladder is pressurized. The outer surfaces of the two jig plates are covered by fiber layers that when placed inside the inner cavity, forms a shear cavity. Located inside the shear cavity may be a piece of core spacer During manufacturing, liquid resin may be infused into the shear cavity, which after curing forms the shear web. In some applications, pre-preg material or film infusion may be used in place of the liquid resin. Surrounding the fiber layers on the upper and lower sections is a flexible membrane that surrounds the inner passageway that surrounds the upper and lower sections to compact the fiber layers and to force the liquid resin, into the inner passageway and the shear cavity.
One drawback with the method disclosed in U.S. Pat. No. 7,473,385 is that liquid resin is not infused completely or uniformly into the inner cavity or the shear cavity. As a result, defects in the part may occur that make the part unusable. Another drawback with this method is that it requires the use two different manufacturing processes—heat/vacuum compaction process and vacuum resin infusion process. The use of these two processes make setup and teardown time longer and more difficult.
What is needed is an improved method for method of manufacturing hollow composite parts formed by compaction with in situ formed internal structures thereby creating parts that are manufactured to design specifications with have fewer defects.